In a NTSC(National Television System Committee) television system, a video signal is divided into a luminance signal Y and chrominance signals, which comprises an I signal indicating hues and a Q signal indicating saturation, and the two chrominance signals I and Q are then modulated by carrier waves of 3.58 MHz for forming carrier chrominance signal. The carrier chrominance signal is combined with the luminance signal Y, then transmitted to a receiver, and separated from the luminance signal Y therein, and, finally, the I and Q signals are separated from each other to be demodulated.
In formation of such a carrier chrominance signal, the I and Q signals are respectively modulated to I carrier wave ICW and Q carrier wave QCW having mutual phase difference of 90.degree.. Accordingly, in the conventional receiver, the separation of the I and Q signals is generally performed by a so-called synchronous detection, that is, the I carrier wave ICW and Q carrier wave QCW are respectively applied to the carrier chrominance signal as synchronizing signal. Here, to digitally perform the synchronous detection, two digital multipliers are needed for applying the carrier waves ICW and QCW respectively corresponding to the I and Q signals in the conventional system. The use of the multiplier, however, causes problems such as low speed of signal processing, enlarged circuit size, and increase in manufacturing cost.